eigenmode frequencies

[C.DARRELL FREEMAN]

hello all,does anybody know if having a mid or high frequency horn driver combo in the throat/mouth area of the 816 series of mid bass enclosure would cancel any effect of the eigenmodes of the affected frequencies in the enclosures passband? this is in reference to the two parallel surfaces that are part of the wooden horn flare.thanks in advance.

[Old Guy]

hello all,does anybody know if having a mid or high frequency horn driver combo in the throat/mouth area of the 816 series of mid bass enclosure would cancel any effect of the eigenmodes of the affected frequencies in the enclosures passband? this is in reference to the two parallel surfaces that are part of the wooden horn flare.thanks in advance.

Have you actually done testing? they aren't that bad, and reducing horn area will further cripple a small horn.

[C.DARRELL FREEMAN]

hello old guy,i have not done any actual testing of the 816 cabinet with appropiate altec woofer.i have heard several that i could find no fault with in this regard.i was basically referring to others post to that effect about the parallel sides of the design causing the effect and was curious.the altec 9864 and the 9894 systems use a variation of the 816 cabinet with the fiberglass horn of the duplex unit mounted in the mouth of the wooden horn flair.i am curious if this additional dimensional shape negates the eigenmode effect.what do you think?anybody else,feel free to chime in.thanks,in advance.

[Alien_Shore]

The 816's published specs are 50-1000 Hz frequency response.
Here is a handy 515 woofer frequency response comparison plot which shows the 816 vs several other bass enclosures, this should give you what you are looking for.

[johnmil]

Sorry to be late to the party. This link should take you to other ALTEC specs.




Index of /images/altec/specs/components

[GM]

hello all,does anybody know if having a mid or high frequency horn driver combo in the throat/mouth area of the 816 series of mid bass enclosure would cancel any effect of the eigenmodes of the affected frequencies in the enclosures passband? this is in reference to the two parallel surfaces that are part of the wooden horn flare.thanks in advance.

The bass horn's eigenmodes will still be there, just at differing amplitudes plus the HF horn will be acting as a crude phase plug which will add a bunch of new ones, but 'chopped up' [much more random, AKA higher order modes], so actually smooths it out somewhat at the expense of a small loss in output due to less horn volume [Vb].

For HIFI apps, adding an open cell foam plug [after Dr. Geddes] will smooth it out further. IIRC he uses 30 ppi.

GM